For many years the deployment of telecommunication systems, for different standards and many frequency bands (for instance 200-300 MHz and 400-500 MHz), has been realized to a large extent by placing radio base stations (RBS) in cellular networks covering large areas. An important link in a traditional radio base station architecture is between the active parts of the system (that is the digital and analog components of the system) to the passive parts (such as the filters and antennas). This high-power analog radio-frequency (RF) link is critical in the sense that it sometimes requires long cables of high quality and large dimensions, in order keep the unavoidable signal quality losses and power losses to a minimum. Such links suffer from the disadvantage of having high costs.
There has been a recent change to integrate the power amplifier and other RF blocks more closely with the physical antenna in order to avoid this critical link, or to reduce the length of the link, which has resulted in what is termed an integrated antenna unit (IAU). The introduction of an IAU implies a change from RF feeders into a high-speed digital interface between a digital processing unit (DPU) and the IAU.
In order to implement a base station today with two or more frequency bands, several complete transmitters are combined on the analogue side after a transmission filter.
Thus, when implementing transmitters for multiple frequency bands, two or more transmitters are implemented in the analogue domain, one transmitter for each frequency band. Similarly, when implementing receivers for multiple frequency bands, two or more receivers are implemented in the analogue domain, one receiver for each frequency band.
This type of technology has a disadvantage in that the multi band transmitters/receivers become bulky, and have low energy efficiency and increased manufacturing cost due to the fact that several complete RF transmitters/receivers in the analogue domain are used to implement the multi band transmitters/receivers.
Furthermore, a radio communication apparatus comprising radio transmitters and radio receivers, as currently known and used in telecommunications networks, comprise transmitter and receiver chains which are set up to work well with a specific range (or “band”) of frequencies only. For instance, a radio unit which works well in the 200-400 MHz range will not work well in the 500-700 MHz range. By the same token, the currently known radio communication apparatus are standard specific which means that one which is used for a GSM compliant telecommunications network cannot be used for an LTE network.
It is possible to add additional transmitter and/or receiver chains of the analogue type described above to enable the radio units to operate at other frequency ranges and/or standards but this has several disadvantages as it makes them bigger, increases their energy consumption considerably and leads to more complex (for instance multi layer) printed circuit boards due to the increased number of analogue and digital components that need to be integrated.
The state of the art analogue RF up-converters used in today's radio units have limited instantaneous bandwidths and are thus not well suited for wideband multi-band operation. Instantaneous bandwidth, IBW, is the bandwidth over which the complete transmitter can process carriers.
Radio units are today implemented by integrating analogue and digital components onto one or more printed boards. The boards tend to be very complex and thus multi layer boards are required. These boards are made out of a very expensive material or a mix of materials, which is even more expensive. Board complexity is primarily caused by the large number of high speed interconnections between components on one and the same board, and also by the number of interconnects/interconnections between different boards. Boards based on traditional technologies are therefore quite complicated, and dissipate a lot of energy, a significant part of which is consumed in the interconnections between the components and boards.